In this study, the emerging methodology of linguistic ethnography is applied to the under-researched setting of the adult numeracy classroom. Students' naturally-occurring discourse is audio-recorded during mathematical collaborative groupwork, and analysed to provide privileged insights not always apparent through observing teacher-led interaction. In particular, the "funds of knowledge" brought by students to their formal learning is investigated, and findings are related to Bourdieu's concepts of cultural capital and habitus, and Bernstein' theories of pedagogic discourse. Participating students were found rarely to draw spontaneously on numeracy funds of knowledge, and tended to ignore the supposedly "reallife" contexts presented by traditional word problems. However, some alternative activities did encourage students to relate classroom learning more to out-of-classroom practices, and the implications of these for pedagogy are discussed. The students were also found to draw on a broad repertoire of linguistic resources to express uncertainty and anxiety; to enhance group cohesion; to elicit contributions from other students; and to ease interactions with humour. However, students additionally brought to the classroom a "schooled habitus" which tended to constrain their discourse and activities to curricular expectations. A categorisation of students' knowledge contributions into "disruptive" and "conformative" is proposed. The study concludes that collaborative groupwork can be highly effective for adult numeracy learners, with participating classrooms demonstrating high rates of retention and achievement, but further research is urgently needed to extend these benefits to students with disabilities, learning difficulties and English as a second language. It further suggests that traditional word problems are not effective in helping learners relate mathematical skills to everyday numeracy practices. However, in introducing innovative and potentially more effective pedagogies, it is recommended that the schooled habitus of adults be taken into account. In particular, pedagogies designed for children and young people may not transfer unproblematically to adult classrooms.